Hello.
As from my side with environment with >20-30 zabbix proxies the next issue is present - if you add new proxy, you forget sometimes to add it into monitoring (for lastaccess and etc).
After adding some internal LLD for zabbix server itself, I suggest you to add zabbix proxy discovery in this case. It helps automatically add monitoring for lastaccess and, probably, zabbix queue on this proxies.
We've already done it for our needs, but it only works for mysql. I suppose, that you have more power for manipulate it
Short part of script:

....
result = run_command('mysql -Ns -e "select host from hosts where status in (5,6);" zabbix')
p_list = result.split('\n')

data = []
for p in p_list:
  data.append({ '{#ZABBIX_PROXY}': p })

json_data = { 'data': data }

print json.dumps(json_data, sort_keys=True, indent=4, separators=(',', ': '))

After that you can create items like {{zabbix[proxy,

,lastaccess]}} and triggers for it.